1. Field of the Invention
The present invention relates to a waterproof main terminal screwed onto an electronic device case.
2. Description of the Background Art
In an electronic device used in a water-entering environment, such as within an engine room of a car, a waterproof main terminal is used to connect an electronic component within an electronic device case to an external device. For an electronic device handling large current, a waterproof main terminal made by insert-molding a metal terminal into a resin housing is often used to connect to an external device via a harness.
One example of conventional waterproof main terminals was an O-ring as presented in Patent Document 1 that is used for waterproofing between an electronic device case and housing of a waterproof main terminal screwed onto the case. Also, waterproofing is needed between a metal terminal and a resin housing because a gap may occur due to difference of linear expansion coefficient. A well known waterproofing method for this case is to apply a chemical agent to the metal terminal and perform edging to increase the creeping distance between the terminal, and the resin of the housing that are insert-molded. Another known method is to apply a special agent to the terminal to join the metal and the resin.
On the other hand, a fluid level detector presented in Patent Document 2 includes a terminal, for electrically connecting a Hall element included in a body as main part to the outside, the terminal being integrally molded with a seal rubber and insert-molded into the body. According to this method, the seal rubber compressively deformed when the body is molded keeps compressed also after molding, generating a surface pressure between the seal rubber and the body. Furthermore, the temperature of the resin increases to high when the body is molded, which causes the seal rubber to adhere tightly to the body. Thus, high sealability is achieved between the seal rubber and the terminal and between the seal rubber and the body.    [Patent Document 1] Japanese Patent No. 4,453,729    [Patent Document 2] Japanese Patent No. 4,089,522
However, the method of performing edging on the metal terminal to increase the creeping distance between the terminal and the housing cannot completely eliminate the gap between the terminal and the housing, so the sealability is incomplete. Furthermore, the method of joining the terminal and the housing limits the material of the terminal and imposes many restrictions to manufacturing, thereby increasing the manufacturing cost.
Furthermore, according to the Patent Document 2, since the body as main part is not screwed onto the electronic device, waterproofing is not performed between the electronic device case and the body. Generally, the waterproof main terminal to be screwed onto the electronic device case requires waterproofing at two locations, or specifically, the O-ring between the case and the housing and a packing between the housing and the terminal. This increases the number of parts and makes fabrication man-hours complicated, thereby increasing the cost.